Components for medical circuits

Abstract

Breathable medical circuit components and materials and methods for forming these components incorporate breathable foamed materials that are permeable to water vapor and substantially impermeable to liquid water and the bulk flow of gases. The materials and methods can be incorporated into a variety of components, including tubes, Y-connectors, catheter mounts, and patient interfaces and are suitable for use in a variety of medical circuits, including insufflation, anesthesia, and breathing circuits.

What is claimed is: 
     
       1. A breathing assistance system comprising:
 a gas source configured to transport a gas; 
 a humidifier configured to humidify the gas from the gas source; 
 a patient interface configured to provide the gas to a patient; and 
 an expiratory limb comprising:
 an inlet and an outlet; and 
 a foamed-polymer conduit that is permeable to water vapor and substantially impermeable to liquid water and bulk flow of gas, the foamed-polymer conduit enabling flow of humidified gases from the inlet to the outlet within a space enclosed by the foamed-polymer conduit, 
 wherein the foamed-polymer conduit is extruded and corrugated, 
 the foamed-polymer conduit comprises a solid thermoplastic elastomer material and cell voids distributed throughout the solid thermoplastic elastomer material, 
 the foamed-polymer conduit has a void fraction greater than 25%, and 
 the foamed-polymer conduit transmits water vapor from the humidified gases within the foamed-polymer conduit to surrounding ambient air through a wall forming at least a portion of the foamed polymer conduit, thereby reducing a build up of condensation within the foamed-polymer conduit. 
 
 
     
     
       2. The breathing assistance system of  claim 1 , wherein the foamed-polymer conduit has a diffusion coefficient of at least 3×10 −7  cm 2 /s. 
     
     
       3. The breathing assistance system of  claim 1 , wherein at least one of the cell voids is connected to another of the cell voids, thereby forming open cell pathways promoting movement of water vapor through the foamed-polymer conduit. 
     
     
       4. The breathing assistance system of  claim 3 , wherein at least 10% of the cell voids are connected to other cell voids. 
     
     
       5. The breathing assistance system of  claim 1 , wherein the expiratory limb further comprises a plurality of reinforcing ribs circumferentially arranged around an inner surface of the foamed-polymer conduit and longitudinally aligned along a length of the foamed-polymer conduit between the inlet and the outlet. 
     
     
       6. The breathing assistance system of  claim 1 , further comprising a heating line along at least a portion of the foamed-polymer conduit. 
     
     
       7. The breathing assistance system of  claim 1 , wherein at least one of the cell voids is flattened along a longitudinal axis extending between the inlet and the outlet. 
     
     
       8. The breathing assistance system of  claim 7 , wherein at least 80% of the cell voids have an aspect ratio of longitudinal length to transverse height greater than 2:1. 
     
     
       9. The breathing assistance system of  claim 1 , wherein the foamed-polymer conduit has a wall thickness within a range of 0.1 mm and 3.0 mm. 
     
     
       10. The breathing assistance system of  claim 1 , wherein the foamed-polymer conduit has an inner volume having an average void size in a transverse direction less than 30% of a wall thickness of the foamed-polymer conduit. 
     
     
       11. The breathing assistance system of  claim 1 , wherein a permeability P of the foamed-polymer conduit is at least 60 g-mm/m 2 /day when measured according to Procedure A of ASTM E96 (using a desiccant method at a temperature of 23° C. and a relative humidity of 90%) and satisfies the formula:
     P >exp{0.019[ln( M )] 2 −0.7 ln( M )+6.5}
 
 
       in which M represents an elastic modulus of the foamed polymer in MPa and M is between 30 and 1000 MPa. 
     
     
       12. The breathing assistance system of  claim 1 , the foamed-polymer conduit comprising an outer skin, adjacent an inner volume, in which the cell voids of the outer skin are closed cell. 
     
     
       13. The breathing assistance system of  claim 1 , wherein the foamed-polymer conduit is sufficiently stiff, such that the foamed-polymer conduit can be bent around a 25 mm diameter metal cylinder without kinking or collapsing, as defined in a test for increase in flow resistance with bending according to ISO 5367:2000(E). 
     
     
       14. The breathing assistance system of  claim 1 , wherein the foamed-polymer conduit is configured to be positioned between a ventilator and the patient and configured to deliver humidified gas to the ventilator from the patient. 
     
     
       15. The breathing assistance system of  claim 1 , wherein the foamed-polymer conduit comprises at least 80% of a length of the expiratory limb. 
     
     
       16. The breathing assistance system of  claim 1 , wherein the solid thermoplastic elastomer material comprises a copolyester material. 
     
     
       17. The breathing assistance system of  claim 16 , wherein the copolyester material has a polyether soft segment. 
     
     
       18. A breathing assistance system comprising:
 a gas source configured to transport a gas; 
 a humidifier configured to humidify the gas from the gas source; 
 a patient interface configured to provide the gas to a patient; and 
 an expiratory limb comprising:
 an inlet and an outlet; and 
 a foamed-polymer conduit that is permeable to water vapor and substantially impermeable to liquid water and bulk flow of gas, such that the foamed-polymer conduit enables flow of humidified gas from the inlet to the outlet within a space enclosed by the foamed polymer conduit, 
 wherein the foamed-polymer conduit is extruded and corrugated, 
 the foamed-polymer conduit comprises a solid thermoplastic elastomer material and cell voids distributed throughout the solid thermoplastic elastomer material, 
 the foamed-polymer conduit has an inner surface adjacent the enclosed space and an inner volume adjacent the inner surface, said inner volume representing a volume of a wall of said foamed-polymer conduit, 
 at least one of the cell voids in the inner volume is connected to another of the cell voids, thereby forming open cell pathways promoting movement of water vapor through the wall of the foamed-polymer conduit, and 
 the foamed polymer conduit further has an outer skin, adjacent the inner volume, in which the cell voids are closed so as to prevent transmission of liquid water and bulk flow of gas. 
 
 
     
     
       19. The breathing assistance system of  claim 18 , wherein the foamed-polymer conduit has a diffusion coefficient of at least 3×10 −7  cm 2 /s. 
     
     
       20. The breathing assistance system of  claim 18 , wherein at least 10% of the cell voids are connected. 
     
     
       21. The breathing assistance system of  claim 18 , further comprising a plurality of reinforcing ribs. 
     
     
       22. The breathing assistance system of  claim 21 , wherein the reinforcing ribs are longitudinally aligned along at least a portion of the foamed-polymer conduit. 
     
     
       23. The breathing assistance system of  claim 18 , further comprising a heating line along at least a portion of the foamed-polymer conduit. 
     
     
       24. The breathing assistance system of  claim 18 , wherein at least one of the cell voids is flattened along a longitudinal axis extending between the inlet and the outlet. 
     
     
       25. The breathing assistance system of  claim 24 , wherein at least 80% of the cell voids have an aspect ratio of longitudinal length to transverse height greater than 2:1. 
     
     
       26. The breathing assistance system of  claim 18 , wherein the foamed-polymer conduit has a wall thickness within the range of 0.1 mm and 3.0 mm. 
     
     
       27. The breathing assistance system of  claim 18 , wherein a permeability P of the foamed-polymer conduit is at least 60 g-mm/m 2 /day when measured according to Procedure A of ASTM E96 (using a desiccant method at a temperature of 23° C. and a relative humidity of 90%) and satisfies the formula:
     P >exp{0.019[ln( M )] 2 −0.7ln( M )+6.5}
 
 
       in which M represents an elastic modulus of the foamed polymer in MPa and M is between 30 and 1000 MPa. 
     
     
       28. The breathing assistance system of  claim 18 , wherein the foamed-polymer conduit is sufficiently stiff, such that the foamed-polymer conduit is configured to be bent around a 25 mm diameter metal cylinder without kinking or collapsing, as defined in a test for increase in flow resistance with bending according to ISO 5367:2000(E). 
     
     
       29. The breathing assistance system of  claim 18 , wherein the foamed-polymer conduit comprises at least 80% of a length of the expiratory limb. 
     
     
       30. The breathing assistance system of  claim 18 , wherein the solid thermoplastic elastomer material comprises a copolyester material.